Re: [boost] Floating Point Utilities Review starts today

Johan Råde wrote:

If I enable SSE2 on VC71 and optimize the code for speed (/O2), then

-std::numeric_limits<double>::quiet_nan()

returns a positive NaN (binary expansion 7ff8000000000000), while

boost::math::changesign(std::numeric_limits<double>::quiet_nan())

returns a negative NaN (binary expansion fff8000000000000).

If I turn off the compiler optimization, then both return a negative NaN.

Conclusion: boost::math::changesign is useful.

Well, if that's the only use, then personally I won't be using it, what use is a negative NaN over a positive one? This feels like a very borderline use case to me, but maybe I'm missing something? John.